The overall objectives of this proposal are to contribute to an understanding of the mode of action of interferon at the cellular level. We propose to investigate events that occur upon interaction of interferon with the cell membrane in order to elucidate more precisely the specificity and the significance of this phenomenon. In previous work we have observed a striking affinity of interferon for cell membrane gangliosides which appears to be specific for carbohydrate constituents of the ganglioside molecule. Furthermore, competition experiments using other proteins with established ganglioside affinity (cholera toxin, tetanus toxin, glycoprotein hormones) result in inhibition of antiviral activity by these substances. However, these experiments do not provide conclusive proof that interferon ganglioside interaction alone is the initiating event of the antiviral response. In fact recent observations suggest that ganglioside-like carbohydrate structures also occur as part of membrane glycoproteins ("ganglioproteins") and that interferon binds to glycoprotein constituents of interferon-sensitive cells. Thus the complete cell membzane receptor of interferon might be composed of both glycoprotein and glycolipid components. It is the aim of this proposal to study more precisely the interferon receptor by: a) isolation of cell membrane glycoprotein components that show specific affinity for the interferon molecule; b) chemical characterization of such components; c) analysis of the determinants for binding to interferon on such isolated membrane cgn tituents; d) investigation of binding properties of modified interferon derivatives to these isolated cell membrane components; and e) specific modification of interferon-binding components in cultured cells without destruction of viability, to determine the effect of such modification on the expression of the antiviral state in vivo.